The ProntoSIL C18 ace-EPS belongs to the new group of stationary RP-supports with polar embedded groups. The packing is very stable over a wide pH range (pH 1-10). In addition, it offers a maximum of hydrophobicity combined with a maximum of polar selectivity. The silanophilic activity of the support is very low. Ultra strong basic compounds such as amitriptyline can be eluted from the column at neutral pH values with excellent symmetrical peak shapes. The main application area of these packings is the pharmaceutical industry, where analytes often have basic or acidic groups. For the separation of these compounds these suppports exhibit an enhanced polar selectivity. That means: In comparison to a classical bonded C18 column acidic compounds show a higher retention whereas basic compounds show a slight decrease of retention on an embedded polar column. The C18 ace-EPS - bonding type is available in several particle and pore sizes.